Over the past sixty years, antibiotics have comprised a key component in both the treatment and prophylaxis of bacterial infections. Since that time the continuous development of new antibiotics has been necessary to limit toxicity, promote broader spectrum therapy, increase convenience of use, and decrease the time to clear the infection. Another driving force in the discovery of new antibiotic agents is the development of microbial resistance and widening gaps in antibiotic coverage. This can most readily be seen in the emergence of antimicrobial resistance to second and third generation fluoroquinolones requiring the subsequent development and application of fourth generation fluoroquinolones. In an effort to stay ahead of resistance, the pharmaceutical industry modifies existing antibiotics and develops new types and classes of antibiotic agents. Protein antimicrobials and agonists respectively represent a new therapeutic approach to ocular surface infection and pathophysiology. Lacritin, a novel human tear protein produced by lacrimal and salivary glands and by epithelial cells of the ocular surface, has multiple functions that encapsulate both areas. It is bacteriocidal for both gram negative and gram positive bacteria at low micromolar concentrations. Also, at low nanomolar concentrations it promotes MUC16 production, cell proliferation and protection against inflammatory cytokines. The discovery of lacritin emerged from a screen for extracellular mediators of lacrimal secretory function. It is a 12.3 kDa glycoprotein, concentrated in lacrimal secretory granules, and has 13 known orthologues. No other organs, beyond the lacrimal functional unit and salivary gland (and possibly the thyroid gland) normally express lacritin. Expression is strongest in lacrimal gland. Lacritin can thus be viewed as an almost exclusive growth factor of the lacrimal functional unit. The lacrimal functional unit is an integrated system comprising the lacrimal glands, ocular surface (cornea, conjunctiva and meibomian glands) and lids, and the sensory and motor nerves that connects them'(2007 International Dry Eye Workshop, Lemp, 2007). Our approach: Based upon these antimicrobial properties elucidated in vitro, we hypothesize that lacritin possesses significant potential as an antimicrobial agent and that topical application of lacritin will augment the native antimicrobial activity in tears. As an ocular-specific presecretory glycoprotein, lacritin has a unique mechanism of action. However, the native glycoprotein, lacritin, may not be the most suitable form. We have prepared several lacritin constructs which may be more suitable with regard to ease of manufacture, stability or efficacy and have selected N-65 lacritin for these proofs of concept studies. The long-term goals Specific Aims for this Phase I proposal include: 1. A demonstration that N-65 lacritin can reduce established Pseudomonas aeruginosa and/or Staphylococcus aureus infections in a rabbit keratitis model. 2. A demonstration that N-65 lacritin can serve as an antimicrobial preservative in topical eye drops. N-65 lacritin may be deemed successful in either or both of our criteria for proof of concept. Our results from these experiments will guide us in defining the scope of commercial development and specific aims for a Phase II proposal. PUBLIC HEALTH RELEVANCE: Antibiotic drops are commonly used to prevent and treat serious eye infections that may result in loss of vision. Although current antibiotics are effective, development of new agents is necessary to ensure that safe and effective treatments are available if resistance develops and renders today's antibiotics ineffective. Our research represents a new therapeutic approach to ocular infection that will evaluate the antibiotic properties of a novel protein in human tears which shows very promising in vitro results with bacteria that cause serious eye infections.